Dihydrogenphosphate recognition: Assistance from the acidic OH moiety of the anion

Abstract

The binding affinity of the acidic hydrogen i.e. OH moiety of dihydrogenphosphate was investigated with receptors having competent H-bond donor and H-bond acceptor component. Three derivatives of 2, 3-dipyrrol-2′-ylquinoxaline substituted with H-bond acceptor moiety at pyrrole α- positions were synthesized and their dihydrogenphosphate affinity was studied. All the three receptors shows general affinity towards fluoride, acetate and cyanide ions in DMSO solution. Interestingly, formyl substitution at both the pyrrole α-positions of 2, 3-dipyrrol-2′-ylquinoxaline leads to binding of H2PO4−. 1H-NMR study rules out the involvement of the H-bond donor unit of the receptor in the biding event and reveals that the binding occurs predominantly via the OH⋯O interaction between the acidic OH moiety of the anion and the CO of the formyl group of the receptor.